Neurogenesis in the adult mammalian brain is restricted to the subventricular zone and the dentate gyrus of the hippocampal formation. These regions contain mitotically active cells that are, in fact, neural progenitor cells (NPCs) with the capability of producing both neuronal and glial cells through adulthood. NPCs are also present in non-neurogenic areas of the adult brain including the neocortex and substantia nigra (SN), and they can give rise to neurons when differentiated under permissive conditions. At present, the physiological role of neurogenesis in the adult brain it is unclear, and the mechanisms underlying this spatial restriction are not yet understood. This proposal will test the overall hypothesis that NPCs from the SN have neurogenic potential, but the SN is a restrictive or non-supportive environment for neuronal differentiation and/or survival. The main goal of this proposal is to investigate whether NPCs from the adult SN can generate functional neurons when exposed to permissive environments both in vitro and in vivo. The Specific Aims cover the characterization of the electrophysiological properties (generation of action potentials and formation of functional synapses) of NPCs cultured in defined media, and co-cultured with astrocytes (known to induce neuronal differentiation) or with primary striatal neurons, the physiological target of dopaminergic neurons from the SN. Furthermore, nigral NPCs will be grafted into the dentate to investigate if they can generate functional neurons in a neurogenic area in vivo. To determine whether there are intrinsic differences between NPCs isolated from neurogenic and non-neurogenic regions, functional properties of differentiated NPCs derived from the SN will be compared with those of NPCs isolated from the dentate gyrus. These experiments will establish whether SN-derived NPCs have the potential to differentiate and integrate in the existing circuits, how their function is influenced by the environment, and whether they can be functionally distinguished from DG-derived neurons. This comparison is relevant to understand the basis for the absence of neurogenesis in the non-permissive environments of the brain.